There are many layers associated with the provisioning of a high availability, robust and scalable telecommunications infrastructure. The switching and transport of the information are two of the atomic functions that such networks need to support, in order for efficient service delivery over large geographical distances. These functions have traditionally been provided using a separate switching (Ethernet silicon switch, ATM switch, SDH cross connect etc.) and a high bandwidth point to point transport pipe (e.g. 10 and 40 G WDM and DWDM technologies).
With the advent of tunable lasers as a displacement technology for traditional distributed feedback lasers, the ability to support flexible optical circuits has allowed a more dynamic and provision centric means of provisioning physical channels within known fibre capacities. Indeed, in next generation optical burst switched (OBS) networks the ability to provide optical packet switch and transport (OPST) capability has emerged as a means of efficient and effective switching and transportation of information between virtually connected endpoints in an optical transmission network, such networks usually adopting a ring topology and wavelength addressed burst. In such a configuration, a physically connected ring constitutes a distributed switch where the wavelength of the light launched from the source lasers creates a virtual path between the ports of said virtual switch. A recent paper entitled “The Optical Switching Revival: Rebuilding Optical Networks for Packets”, Heavy Reading, Vol. 7, N. 3, March 2009 discloses this virtual switch concept and where the next generation optical burst switched (OBS) networks is heading towards.
Traditional circuit switched telecommunication systems operate on the basis of fixed dedicated communication channels being available permanently for the launching and reception of information. The integrity of such communication paths are monitored in a number of different schemes, for example, SONET\SDH has J0,J1,J2, which are used to generate TIM Trace Identifier Mismatch, telecommunications standard G709 which has Trail Trace Identifier (TTI); IP\MPLS has Bidirectional Forwarding Detection—BFD and/or Ethernet has emergent 802.1ag\Y1731. In these schemes quanta of information are launched, via specific probe packets, into the system as a means of ensuring continuity of the channel for information exchange purposes, where the channel in this instance is a messaging or higher level entity for continuity and connectivity checking between higher level communicating functions embedded within terminal devices of the network.
OBS communication networks, in the general case, access the physical channel in an asynchronous temporal manner. That is to say, access to the communication channel is not aligned to any system timing boundary and where such access is derived by the dynamic traffic load. Due to the highly aperiodic nature of the proposed access mechanism to the physical transport infrastructure, in true OBS networks, there is a need to ensure that the high level control functions of the network have visibility as to the condition of the physical plant on a continuous basis so that it is fully aware of all link and path availability before using such infrastructure. In an asynchronous OBS network, where there may be long periods of inactivity before a given path in the network is used, it is a critical need for the high availability of the system that silent failures do not occur and that asynchronous, aperiodic, OBS paths are probed on a time bounded basis. A silent failure refers to the situation where a failure of the path is not detected through the loss of data, due to the potentially long periods of inactivity on an OBS path. Without such a deterministic mechanism, as proposed, any OBS based transmission network is prone to silent failure events and to less than adequate resiliency for carrier class deployment.
Optical communication systems based on Dense Wavelength Decision Multiplex technology exhibits wavelength dependent performance. In wavelength addressed optical burst networks, services that overlay such infrastructure require that all wavelengths within the networks maintain a minimum level of performance so as to ensure that the overall virtual switch paths remain colourless. Colourless operation referring to the wavelength independent nature of each path in such a virtual switch, i.e. any colour can be assigned to perform the data carting task on any path of the switch. Each path is assigned a specific wavelength, with each node or switch in the network is configured to transmit/receive a particular wavelength.
Typically in a ring network data is scheduled onto such virtual wavelength addressed switches in an asynchronous fashion so that all nodes have fair access to the switch fabric. The path monitoring function is performed at the highest scheduled priority level and in a periodic manner, by default. This type of scheduling is disclosed by PCT Patent Publication Number WO2004040722, filed by the same applicant as the present application, Intune Networks Limited.
There is therefore a need to provide physical path monitoring of virtual paths in optical burst switched networks, so as to provide a highly available network infrastructure for delivery of flexible network services, which overcomes the above mentioned problems associated with OBS networks.